The present relates generally to pressure gauges and more specifically to pressure gauges having means integrated therein to confine corrosion contamination within the gauge from contaminating the fluid that is being measured.
While having other applications, the present invention is especially useful in the medical field in which balloon catheters are used. Balloon catheters, as known in the medical art, have various applications in which an inflatable balloon on the end of a catheter is inflated and/or deflated in the body of a patient. The inflation of such balloon is accomplished by a fluid, either a gas or liquid, and typically the pressure of such fluid is monitored. Although, in normal operation, the balloon and corresponding catheter provide a fluid-tight seal between the pressure-inflating fluid and the patient, there always remains the risk that the balloon and/or catheter supplying the balloon would develop a leak, causing the pressurized fluid to come in contact with the tissue of the patient. Should there be a contaminant in the pressurized fluid used to inflate the balloon catheter, such a leak would jeopardize the health of the patient.
Frequently, the balloon at the end of the catheter is located in a vessel in the patient's body and is not readily visible to the doctor utilizing the balloon catheter. Consequently, appropriate control over the balloon catheter is maintained by monitoring the pressure of the fluid supplied to the balloon. By previous experimentation, it is possible for the medical doctor to know how large the balloon will inflate as a function of the pressure in the fluid. Such fluid is typically monitored by a pressure gauge placed in series along the lines supplying pressurized fluid to the balloon. Unfortunately, a problem exists as to corrosive material from within the mechanical pressure gauge leaking into the pressurized fluid and migrating to the part of the balloon catheter located within the patient. Such contamination typically takes the form of corrosion and acid present from the use of acid flux in soldering and/or welding internal components of the pressure gauge. Typically, such pressure gauges are made of brass, resulting in a corresponding green corrosion mixed with the acid flux residue. This corrosion forms a "green goo" which, in some circumstances, can migrate into the balloon catheter, increasing the risk of contamination of the patient.
Efforts have been made to solve this problem, but have met with limited success. For example, some have tried compartmentalizing gold-plated nickel bellows in the pressure gauge to isolate the inner volume of the pressure gauge from the main line to which the gauge is attached. Unfortunately, this approach breaks down easily, is relatively expensive, and does not survive the necessary repeat sterilization of the pressure gauge. The bellows become degraded during sterilization, which is imperative in the medical field, resulting in an unsatisfactory design. Other approaches include attempts to use solvents and techniques to rinse the corrosion and acid flux residue from the pressure gauges. So far as is known to the inventor, this approach has had unsatisfactory results. Other rubber diaphrams have been unable to survive repeated sterilizations.
Various pressure gauges have been disclosed in United States patents. U.S. Pat. No. 2,986,938 to Grandstaff discloses a pressure gauge having a flexible diagram providing a seal between the fluid being measured and the pressure gauging device. Also, Grandstaff has a piston with O-rings and a longitudinal bore down the center of the piston. However, this longitudinal bore is plugged. U.S. Pat. No. 2,498,366 to Greer discloses an automatic gauge valve having a piston (reference no. 23) which acts as a valve body to regulate fluid flow. This piston includes a passage therethrough communicating the pressure gauge with the supply of pressurized fluid. The passage therethrough is obstructed by a check valve ball having a spring bias. U.S. Pat. No. 4,370,982 to Reilly discloses a device for inflating balloon catheters with a pressure gauge coupled thereto. U.S. Pat. No. 3,496,776 to Mistarz discloses a pressure gauge having a flexible diaphragm to seal contaminants in the pressure gauge from entering the measured fluid, such as milk. U.S. Pat. No. 2,841,984 to Green discloses a pressure gauge having a flexible membrane for transmitting fluid pressure. U.S. Pat. No. 3,415,123 to Broughton discloses a device having a piston mounted within a body member to be connected between an oil well drilling pipe and a pressure gauge to prevent drilling mud from entering the pressure gauge while allowing the drilling mud pressure to be transmitted to the gauge. U.S. Pat. No. 3,975,967 to Conti discloses a corrosion resistant bourdon tube used in a pressure gauge. While each of these devices provide certain advantages, none of them provide the same advantages in the same way as the present invention.
The present invention solves the problem of isolating the corrosion and other contamination from the main line to which the gauge must necessarily be attached and still assure reliable, accurate pressure gauge readings, following multiple sterilizations.